The production of such fatty acid esters has long been known. It is effected on an industrial scale mainly by the base-catalyzed transesterification of fatty acid glycerides with lower alcohols. The procedure basically being such that the fatty acid glycerides are brought into contact with the lower alcohol in the presence of a basic catalyst at reaction conditions differing as a function of the starting material. The reaction mixture, once the transesterification is completed, separating into a heavy phase of more or less pure glycerol and a light phase consisting of the fatty acid esters of the lower alcohols.
The reaction conditions depend on the respective type of fatty acid glycerides employed. It is known, for instance, that oils and fats of natural origin, such as they are normally used, depending on their origin and pretreatment, have a content in fatty acids in the free state of up to 20 percent and more, can be transesterified in the presence of basic catalysts at temperatures around 240.degree. C. and a pressure of about 100 bar at a seven to eight-fold molar excess of alcohol. (Ullmann, Enzyklopadie d. techn. Chemie, 4th edition, vol. 11, page 432 (1976)).
It is further known that such transesterification can be carried out at temperatures around the boiling point of the alcohol used and at normal or only slightly increased pressure at slight excess of the lower alcohols if the oils and fats employed are first deacidified by methods such as distillation, alkali extraction, acid-catalyzed preesterification and the like to a maximum content in free fatty acids of 0.5 percent and are subsequently dried.
It is further known that oils and fats are transesterified at normal pressure and environmental temperature with stoichiometric amounts of the lower alcohols in the presence of 1.0 to 1.7 percent by weight of potassium hydroxide based on the weight of the fat or oil employed. A substantial share of the known processes is dedicated to the purification of the fatty acid esters, in particular the elimination of the catalyst used.
The substantial drawbacks of the known processes reside in the fact that in the case of the application of high temperatures and pressures as well as excesses of alcohol, expensive reactors are necessary and high energy costs are incurred. Otherwise, the oils and fats used will have to be deacidified and dried, which also calls for expensive equipment. Additionally, the degrees of transesterification are too low and/or the contents in residual glycerol are too high, which is particularly the case in processes employing low alcohol excesses or stoichiometric amounts of alcohol, which for most intended uses calls for a subsequent distillation of the fatty acid esters. The removal of the catalyst, if this is effected by washing with water, causes considerable difficulties in the subsequent phase separation due to the formation of emulsions, or, if the catalyst is removed by washing with acids, a considerable amount of fatty acids in the free state is transferred to the ester phase. Further, in case an ion exchanger is used, the drawbacks connected with the regeneration and the effluents accumulating thereby must be coped with.
A further disadvantage common to all the known processes is that they can only be carried out by means of expensive or elaborate equipment and the technical expenditure connected therewith. Thus, they are economically unfeasible in small and minimum scale systems.
As a result, there was a demand for a process which is free of the aforementioned drawbacks and permits the production of such fatty acid esters from fatty acid glycerides of any given origin in purified or unpurified form especially with high contents in fatty acids in the free state at ambient temperatures and atmospheric pressure and the lowest possible alcohol excesses at any given and nearly one hundred percent degrees of transesterification at a minimum of technical and equipment expenditure, which process was to be suitable for large industrial systems as well as small and minimum scale systems.